Baby P's mother is due to be sentenced alongside the two men also convicted over the little boy's brutal death.
The trio have been warned that they face substantial prison sentences when they appear before Judge Stephen Kramer at the Old Bailey.
The mother, 27, begged the judge for mercy on Thursday as she apologised for "letting down" her "darling" son.
Baby P, who can now be named as Peter, was 17 months old when he was found dead in a blood-spattered cot in August 2007 having suffered a broken back and fractured ribs.
He had more than 50 injuries despite being on the at-risk register and receiving 60 visits from social workers, doctors and police over eight months.
The mother, her boyfriend, 32, and their lodger, Jason Owen, 37, of Bromley, Kent, face up to 14 years in jail for causing or allowing Peter's death.
But the mother is likely to get a shorter sentence because she pleaded guilty to the offence - and the term will also be reduced by the 21 months she has already spent in custody.
The boyfriend could receive a life sentence after being convicted of raping a two-year-old girl.
Peter's mother wrote a letter to the judge from prison that was read aloud in court yesterday. In it she said sorry for the pain and suffering she had caused and begged her family, including Peter's natural father, for forgiveness.
Peter's natural father told the Old Bailey on Thursday of his horror at the knowledge that the little boy suffered months of pain, fear and loneliness before his death. He said his life had become a "living nightmare" since losing his son.
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